Generators are used in motor vehicles for converting mechanical energy into electrical energy. Most of the generators used for this purpose in motor vehicles are synchronous generators configured as claw pole generators.
In hybrid drive technology for motor vehicles, synchronous machines are also operated in motor operation in order to start the internal combustion engine of the hybrid drive system. For this purpose, the synchronous machine may be configured as a belt-driven starter generator (BSG) for the start/stop operation. Such a starter machine is usually operated as a motor only at very low engine speeds because the torque that is able to be generated drops rapidly over the engine speed. In order to increase the output, modified synchronous machines are operated in a 48V vehicle electrical system.
Conventional generators such as synchronous generators configured as claw pole generators have a generator regulator or a current regulator which regulates the exciting current in order to set the power output of the generator. The checking of a current sensor for measuring the exciting current is not provided. However, during the transition to a 48V vehicle electrical system it must be ensured for safety reasons, due to the higher torque output in a motor operation of the synchronous machine, that an unintended torque output due to incorrect exciting current measurements are prevented in a reliable manner, for the synchronous machine is normally used in a boost-recuperation system at a much higher output, both in a motor and a generator operation, which causes clearly higher brake torques or propulsive forces to be generated.
A device is known from US publication 2007/0085512 A1, for controlling the voltage of a generator, which includes an arithmetic unit which includes a functionality for correcting the exciting current. This is done on the basis of the current flow into an electrical load to which the voltage of the generator is applied, and on the basis of the output current of the generator calculated on the basis of the exciting current.
Patent document U.S. Pat. No. 4,413,222 discusses a battery charging system which has an alternating current generator (10), a voltage regulator (20), and a charge control device for indicating malfunctions. This device is connected to a signaling device (82) for detecting the switching state of the voltage regulator, a first threshold stage (67) for detecting a minimum value of the generator voltage and a second threshold stage (69) for detecting a voltage that is above the regulation setpoint value by a specific value at a sensing point of the system. The one input of the first threshold stage (67) is connected to a fault detection connection (D+), which is decoupled from the battery voltage, at the exciting system (12, 14) of the generator. The second threshold stage (69) is connected on the input side to a sensing point that is affected by the battery voltage. This has the advantage that the first threshold stage (67) is able to record and evaluate the generator voltage in an unbiased manner, unaffected by the charge state of the battery, and the second threshold stage.